Thread trimmer for blind stitch sewing machine

ABSTRACT

A thread trimmer for a blind stitch sewing machine used in conjunction with a needle positioning mechanism, the thread trimmer utilizing a reciprocating thread puller/clamp and reciprocating cutter blade simultaneously actuated by the pistons of single acting air cylinders under the control of a foot operated electrical switch, the thread puller/clamp completing its function prior to actual severance of the thread by the cutter. The sewing machine bed plate is automatically dropped by an air cylinder just after trimming completion to clear the bed and permit insertion of new work for stitching, the air cylinder being also actuated by the foot operated electrical switch. Control circuitry interconnects the thread trimmer and needle positioning mechanism to insure that neither trimming nor needle positioning can take place during normal stitching, that trimming cannot take place during needle positioning, and that trimming cannot take place unless the sewing machine needle and looper are in particular positions.

United States Patent Koschoif et al.

[54] THREAD TRIMMER FOR BLIND STITCH SEWING MACHINE [72] Inventors: John Koschofi, Centralia; Kenneth C. Haas, Mohnton; Robert F. Pettit, Reading,

all of Pa.

[73] Assignee: Teledyne, Inc., Los Angeles, Calif.

[22] Filed: Dec. 18, 1970 [21 1 Appl. No.: 99,590

521 user ..112/252 51 lnt.Cl. D05b65/02 [451 May 30, 1972 Primary Examiner-James R. Boler Attorney-Edelson and Udell [57] ABSTRACT A thread trimmer for a blind stitch sewing machine used in conjunction with a needle positioning mechanism, the thread trimmer utilizing a reciprocating thread puller/clamp and reciprocating cutter blade simultaneously actuated by the pistons of single acting air cylinders under the control of a foot operated electrical switch, the thread puller/clamp completing its function prior to actual severance of the thread by the cutter, The sewing machine bed plate is automatically dropped by an air cylinder just after trimming completion to clear the bed and permit insertion of new work for stitching, the air cylinder being also actuated by the foot operated electrical switch. Control circuitry interconnects the thread trimmer and needle positioning mechanism to insure that neither trimming nor needle positioning can take place during 7 normal stitching, that trimming cannot take place during needle positioning, and that trimming cannot take place unless the sewing machine needle and looper are in particular positions.

10 Claims, 8 Drawing Figures Patent ed May 30, 1972 3,665,878

5 Sheets-Sheet 1 k w INVE/W'ORS Jaw v laSc/MFF KENNETH C, #445 FIG. I Q foaa'er FT Parr/7 WM M Patented May 30, 1972 5 Sheets-Sheet 2 Z S Rcqp 0 TOHF 3 V 2 WW .2; Z2 7 Patented May 30, 1972 5 Sheets-Sheet 5 5 Sheets-Sheet 5 Patented May 30, 1972- i INVENTORS JOHN KOSCHOFF 4 Has 4 rrakwtrs THREAD TRIMMER FOR BLIND STITCH SEWING MACHINE This invention relates generally to blind stitch sewing machines, and more particularly relates to thread trimming mechanisms for such sewing machines.

Thread trimming in sewing machines is of itself fairly well developed, particularly with respect to the vertically reciprocating type of sewing machine needle in which thread trimmers are operated in conjunction with needle positioning mechanisms which cause the thread trimming to be carried out after the sewing machine needle has been moved out of the work to its raised or upper position. Blind stitch sewing machines are of course structurally different from vertically reciprocating needle types of sewing machines and include a looper device as part of the stitch forming mechanism. The looper mechanism of the blind stitch sewing machine is located right at the stitch forming region above the work and the sewing machine presser foot, and must be in such rotated position that the needle thread is properly presented for severance. Fortunately, this position of the looper device occurs when the sewing machine needle is retracted from the work and is not in a position of interference with respect to the thread severing device to be described.

The proper positioning of the looper and the needle is effected by means of a needle positioning mechanism coupled to the sewing machine drive, the needle positioner being automatically effective at the end of each stitching sequence to stop the sewing machine in proper position for thread trimming regardless of whether or not thread trimming is thereafter actually carried out. A control mechanism for the system is so arranged that the thread trimmer and the sewing machine bed-drop mechanisms cannot be actuated until the needle positioner has completed the proper positioning of the needle and the looper. Additionally, any attempt to trim the thread or drop the work supporting bed interrupts the functioning of the needle positioner and thereby disables the entire apparatus. The needle positioner must be allowed to complete proper positioning in order to thread trim or drop the worksupporting sewing machine bed.

One other consideration of substantial importance is the avoidance of unthreading of the needle after a thread trimming operation when the sewing machine is subsequently activated for a new stitching run. Unthreading of the needle will normally occur after thread trimming in the absence of precautions to the contrary because insufficient needle thread length remains to permit securement of the thread in the work when the first stitch is taken after trimming. Accordingly, a novel thread puller and thread'lock constitute an important part of the invention and function to pull additional thread from the thread supply prior to the trimming operation so that sufficient slack exists in the needle thread to prevent unthreading of the needle on the subsequent stitching operation.

It is accordingly a principal object of the invention to provide a novel thread trimming device for a blind stitch sewing machine which incorporates a novel thread puller and thread locking device to prevent unthreading of the sewing machine needle after a thread trimming operation.

Another object of the invention is to provide a novel thread trimming mechanism for a blind stitch sewing machine as aforesaid which incorporates a novel control mechanism which prevents thread trimming or dropping of the work-supporting bed of the sewing machine until the needle and looper mechanisms of the sewing machine have been properly positioned by an automatic needle positioner used in conjunction with the trimming mechanism.

It is a further object of the invention to provide a novel thread trimming mechanism for blind stitch sewing machines in which the control mechanism disables the entire apparatus if an attempt is made by the operator to trim the needle thread before proper positioning has taken place.

The foregoing and other objects of the invention will become clear from a reading of the following specification in conjunction with an examination of the appended drawings wherein:

FIG. 1 is a front elevational view of the machine with the thread trimming and thread pulling devices mounted thereto;

FIG. 2 is a plan view of the apparatus of FIG. 1 as would be seen when viewed along the line 2-2 of FIG. 1;

FIG. 3 is a fragmentary perspective view from above and behind on an enlarged scale of the thread trimmer and thread clamping devices carried on their mounting bracket;

FIGS. 4 through 7 are a sequence of perspective views showing the operative ends of the thread trimmer and thread puller devices as well as the sewing machine needle tip and looper device as a complete trimming cycle is carried through; and

FIG. 8 is a schematic electrical diagram of the thread trimmer and needle positioning mechanisms together with their control circuitry.

In the several figures, like elements are denoted by like reference characters.

Referring now to the drawings, and first to FIGS. 1 to 3, there is seen a blind stitch sewing machine designated generally as 10 having a spindle shaft 11 driven through a belt system from a motor drive 12 which includes a needle positioning mechanism and control devices to be subsequently described in connection with the circuit diagram of FIG. 8. The spindle shaft 11 is internally connected through the normal sewing machine mechanism to cyclically oscillate the sewing needle 13 and the sewing machine looper 14 to repetitively produce blind stitches in the fabric 15 which is positioned between the bed plate 16 and presser foot 17. The needle thread 18 runs upward from the needle 13 through the thread guide 19, thread puller and clamp 20, and thread tensioning discs 21 to a thread supply (not shown).

The thread puller 20 is carried on a bracket designated generally as 22 which is secured to the top of the sewing machine by studs 23, as best seen in FIG. 2, which bracket 22 also has secured thereto a thread cutter support housing 24 which carries the thread cutter designated generally as 25. The thread puller 20 and the thread cutter 25 are both pneumatically operated devices of the single acting piston type in which the piston is retracted by a spring operator when the pressurizing fluid isdepressurized. In the embodiment illustrated, the pneumatic cylinders are actuated by compressed air through the air lines 26 which connect to a solenoid actuated air valve 27 illustrated in the circuit diagram of FIG. 8.

Another pneumatic cylinder 28 is connected to the compressed air source through air line 29 and solenoid actuated air valve 30, which latter is also illustrated in the circuit diagram of FIG. 8. The pneumatic cylinder 28 is connected through a linkage, as best seen in FIG. 1, to the bed plate 16 of the sewing machine and is effective when actuated to drop the bed plate by pivoting it downward about the end pivots 31 to thereby drop the work 15 from beneath the needle and presser foot.

Turning now to FIGS. 3, 4 and 5, it is observed that the thread puller 20 includes an L-shaped angle piece 32 to the vertical wall of which is fixedly secured the pneumatic cylinder 33 by means of nut 34, with the cylinder piston 35 extendable through the angle piece vertical wall for reciprocating movement above and parallel to the horizontal wall of the angle piece 32. Afiixed to the end of the piston 35 is a U-' shaped clamp 36 provided with a pair of aligned holes 37 in the clamp side walls through which runs the needle thread 18. The inner face of the base of the U-shaped clamp 36 has secured thereto a compressible pad 38, the holes 37 being spaced sufficiently away from the base wall of the clamp 36 so that the thread 18 is not engaged by the pad 38 during normal stitching, as for example best seen in the showings of FIGS. '2 and 4.

Fixedly secured to and extending upward from the horizontal wall of the angle piece 32 are a pair of side pins 39 and a clamping post 40. The side pins 39 are positioned immediately outside of the arms of the U-shaped clamp 36 on opposite sides thereof while the clamping post 40 is positioned centrally between the arms of the clamp 36, both of the side pins 39 and the clamping post 40 being on the same side of the thread 18 with the clamping post 40 positioned away from the pins 39 by a distance at least equal to one-half of the length of the needle thread which it is desired to pull from the thread supply prior to thread trimming in order to provide the necessary slack to avoid unthreading of the needle on the subsequent stitch.

From the showing of FIG. it will be appreciated that the length of thread actually pulled from the thread supply is twice the length of thread extending from one of the clamp holes 37 to the rear of the adjacent pin 39. It will also be appreciated from the showing of FIG. 5 that when the thread puller and clamp is actuated, the pad 38 presses the thread 18 against the clamping post 40 to hold the thread taut to insure severance by the thread trimmer. The frictional engagement of the thread with the clamping structure also reduces the tendency of needle thread snap-back as the clamping pressure is released after thread severance.

The thread cutter includes a pneumatic cylinder 41 having an extensible and retractable piston 42 to the outer end of which is secured a blade carrier 43 by means of a nut 44. Adjustably projected through the blade carrier 43 and secured in desired position by a set screw 45 is a trimmer blade 46 formed with a recessed cutting notch 47. As best seen in FIG. 6, when trimming occurs, the cutting notch 47 of the trimmer blade 46 severs the portion of the thread which extends under and upward around the lower leg of the looper 14 after emerging from the fabric 15. This not only minimizes the thread tail extending from the fabric, but also maximizes the thread tail 18a which extends beyond the eye of the needle 13 to thereby aid in avoiding unthreading of the needle as the next stitch is taken.

FIG. 4 illustrates the thread puller and thread cutter in their deactuated positions during normal stitching by the sewing machine. In this condition it is observed that the thread 18 runs freely from the thread supply through the thread puller 20 and to the needle 13, while the trimming blade 46 is retracted out of the way of the stitching mechanism. When trimming is desired, the sewing machine operating treadle is heeled to actuate the trimming circuitry in a manner which will be described subsequently in connection with the showing of FIG. 8. This causes both the thread pulling and trimming cylinders 33 and 41 respectively to be pressurized to thereby drive the pistons and 42, as seen in FIG. 5.

From the showing of FIG. 5 it is observed that the stroke of the piston 35 is arranged to be shorter than the stroke of the piston 42 in terms of operatively carrying out their respective functions, so that the thread 18 is pulled from the thread supply and clamped against the post by the pad 38 of the clamp 36 at a time when the trimmer blade 46, while extended, has not completed its travel to sever the thread 18. FIG. 6 illustrates the conditions immediately thereafter in which the trimmer blade 46 has completed its travel and severed the thread 18 while the thread remains clamped by the thread puller and clamp 20. FIG. 7 illustrates the conditions immediately following those shown in FIG. 6, in which the thread puller and clamp 20 and the thread cutter 25 have been automatically deactivated and returned to their original positions.

Also illustrated in FIG. 7 is the pivotal dropping of the bed plate I6 from the dotted line position representing the position of the plate during normal sewing to the solid line position illustrating the position of the bed plate for removal of the stitched article and in preparation for insertion of the next item to be stitched. As will be subsequently seen, the bed plate 16 remains in its dropped position as long as the operator maintains the sewing treadle in the heeled position and returns to its raised horizontal position when the treadle is released. The thread puller 20 and thread cutter 25 however, as previously described, automatically return to their positions as shown in FIGS. 4 and 7 regardless of whether or not the treadie is in its heeled position or has been released, and this will become clear from an examination of the circuit diagram of FIG. 8 to which attention should now be directed.

The schematic diagram at FIG. 8 encompasses two basic sections, one being that portion of the apparatus which is concerned with needle positioning, while the other portion of the apparatus is concerned with thread trimming and dropping of the sewing machine bed plate. Necessarily, there are of course interconnections between the two sections, and both sections utilize parts of the same power supply. The power supply includes the terminals 48 which are connectable to a power source of alternating current, the bridge rectifier 49, stepdown transformer 50 and full wave rectifier 51 together with the conductors which interconnect these elements to the source of power.

The needle positioner portion of the apparatus includes treadle switch 52, pole 53 and contact 54 of relay 55, brushes 56 and 57 and rings 58 and 59 of synchronizer device 60, pole 61 and contact 62 of relay 55, relays 63 and 64, drop out delay device 65 and needle positioning motor 66. The needle positioner aspects of the control mechanism are essentially the same as those of the needle positioning mechanism previously illustrated and described in US. Pat. No.2,96l,59l assigned to the assignee of the present invention, a brief description of which now follows.

The synchronizer 60 includes a rotor which has a plurality of rings, of which ring 59 is completely conductive regardless of the rotated position of the synchronizer and in which others of the rings are conductive in the arcuate regions shown in heavy line while being nonconductive in the arcuate portions shown in lighter line. This ring assembly is concentrically mounted to the spindle shaft of the sewing machine and rotates therewith while a brush holder which carries the brushes which engage the rings is mounted in fixed position with respect to the sewing machine so that the rings rotate past the brushes as the sewing machine spindle shaft rotates. Since one revolution of the spindle shaft corresponds exactly to one complete stitch forming cycle, the positions of the sewing machine needle and looper always correspond to unique positions of the rotatable rings. Accordingly, the brushes of the. synchronizer can be positioned so that when the needle and the looper are in particular positions, the brushes will be engaged with particular portions of the rings, as for example a conductive portion or a nonconductive portion.

The positioning motor 66 is of the direct current type and has its field winding and armature both energized for driving movement by the motor for positioning the sewing machine needle and incorporating dynamic braking by having its armature short-circuited while the motor is rotating with its field winding still energized. The control of the positioning motor is carried out by the relays 63 and 64 together with the drop out delay circuit 65.

When the sewing machine operator finishes a stitching sequence and releases the operating treadle, the switch 52 closes as illustrated in FIG. 8 to thereby establish a current flow path through pole 53 and contact 54 of relay 55 to synchronizer brush 56. Ifthe sewing machine has stopped with the needle-13 and looper 14 in the desired positions for thread trimming, then the brush 56 will be in contact with a nonconducting segment portion of the ring 58, also as shown. In this event, there can be no current flow from the brush 56 into the ring 58 so that the needle positioning motor cannot be energized and no change in the positions of the needle and looper will occur.

If however the needle 13 and looper 14 have come to rest in a nondesired position, then the synchronizer brush 56 will be in contact with an electrically conductive portion of the ring 58 and current will flow from the power supply through the path previously traced to the brush 56, into ring 58 and then to center conducting ring 59 through the shorting link 67, thence outward through brush 57, pole 61 and contact 62 of relay 55 to energize the relay 63. When relay 63 pulls in it also pulls in relay 64, energizes the dropout delay circuit 65, which typically may be a capacitor, and also removes a short circuit across the positioning motor armature so that the positioning motor when energized may drive the sewing machine and consequently also rotate the synchronizer rings. The pull-in of relay 63 energizes the field and armature windings of positioning motor 66.

Rotation of the synchronizer rings continues until brush 56 runs ofi of the conductive portion of ring 58 and onto a nonconductive portion which then interrupts the flow of current to relay 63. When relay 63 drops out, it automatically applies a short circuit across the armature of positioning motor 66. However, the field winding of the motor 66 remains energized for a time because the dropout delay 65 temporarily maintains relay 64 in an energized state. Dynamic braking of the positioning motor 66 therefore occurs which stops the motor and consequently the sewing machine within the nonconductive interval of the ring 58. Relay 64 thereafter drops out and deenergizes the positioning motor windings.

The needle and looper of the sewing machine have now of course been properly positioned for thread trimming, and trimming can be carried out when desired by heeling the sewing machine treadle to thereby close switch 68 to energize coil 69 of relay 55 and thereby transfer relay pole 53 from contact 54 to contact 70 and transfer relay pole 61 from contact 62 to contact 71. The transfer of poles 53 and 61 of relay 55 prevents operation of the needle positioning mechanism by open circuiting the relays 63 and 64, and also establishes conditions such that the coil 72 of trimming relay 73 may be energized through the synchronizer 60, thereby insuring that trimming cannot take place unless the synchronizer is in properly rotated position corresponding to the desired positions of the needle 13 and looper 14. Additionally, it should be noted that when relay 64 had been energized during needle positioning, pole 74 of the relay had been moved out of contact with contact 75, so that under no possible circumstance could the solenoid actuated air valve 30, which drops the sewing machine bed plate 16, be energized until the needle positioner has come to rest and relay 64 has dropped out. This functional interconnection between a portion of the positioning circuit and the bed plate dropping circuit constitutes one of the safety lock-outs of the system.

Turning now to the trimming portion of the circuit in more detail, it is observed that the'positive terminal of the bridge rectifier 49 is connected through appropriate conductors and a current limiting resistor 76 to a normally closed contact 77 of relay 73 through the contact 77 and associated relay pole 78 to the positive terminal of a capacitor 79. The negative terminal of the capacitor 79 is returned to the negative terminal of the bridge rectifier 49 through pole 80 and normally closed contact 81 of the trimming relay 73. Consequently, when the trimming relay 73 is deenergized corresponding to its quiescent or non-trimming state, the capacitor 79 charges to its maximum potential.

When coil 72 of trimming relay 73 is energized to carry out a trimming operation, relay poles 78 and 80 respectively transfer from their normally closed contacts 77 and 81 to their normally open contacts 82 and 83 thereby breaking the capacitor charging circuit and discharging the capacitor 79 directly through the coil 27 of the solenoid actuated air valve which actuates the thread puller and thread cutter 25. Actuation of the thread puller and the thread trimmer takes place as previously described, and when the charge on the capacitor 79 has fallen to a point insufficient to maintain the coil 27 in its energized state, the latter deenergizes and therefor deactuates the thread puller and thread cutter regardless of the fact that the trimming relay 73 is still in its pulled-in state.

When the trimming relay 73 was pulled in, its third pole 84 closed against normally open contact 85 to thereby energize the coil 30 of the solenoid actuated air valve which pressurizes the pneumatic cylinder 28 to cause sewing machine bed plate 16 to be dropped, as previously described. The sizes of the pneumatic cylinders 33 and 41 associated with the thread puller and thread cutter are much smaller than the pneumatic cylinder 28 which actuates the bed plate 16 since the masses to be movably controlled are also respectively much smaller and lighter. For this reason the thread pulling and trimming operations are completed before the bed plate 16 begins its downward movement. Unlike the trimming mechanisms however, the bed dropping solenoid remains energized as long as the trimming switch 68 is closed so that the sewing machine operator may conveniently remove the fabric and insert a new piece of work prior to releasing the trimming switch 68 and permitting the bed plate 16 to again rise to operative sewing position.

The second safety lock-out circuit for the trimmer mechanism is provided by the electrical interlock between the synchronizer 60 and the trimming relay coil 72. It will be recalled that when the trimming switch 68 was closed to thereby energize the coil 69 of relay 55, the relay poles 53 and 61 were transferred to their respective contacts 70 and 71. This establishes the current flow path for energization of the trimming relay coil 72 from the rectifiers 51 through the treadle switch 52, through the pole 53 and contact 70 of relay 55 to synchronizer brush 86, thence from the brush 86 into the conductive portion of ring 87 and through synchronizer shorting link 67 to conductive ring 59, thence outward through the synchronizer brush 57 to a pole 61 and contact 71 of relay 55 to trimming relay coil 72 and its return to the transformer power supply.

As previously noted, the synchronizer 60 is illustrated with its brushes and rings corresponding to a properly positioned needle and looper of the sewing machine so that the current flow path just traced permits trimming to take place. If however, for whatever reason, the synchronizer rings were misaligned with the brushes so that brush 86 was not in contact with the conductive segment of ring 87, then the current flow path to coil 72 of the trimming relay would be interrupted and energization of the trimming relay could not take place. Accordingly, it will be appreciated that by routing the energization circuit of the trimming relay through the synchronizer 60, the trimming function is locked out unless the sewing machine needle and looper are in their proper and desired positions.

Having now described our invention in connection with a particularly illustrated embodiment thereof, it will be appreciated that modifications and variations of our invention may now occur from time to time to those persons normally skilled in the art without departing from the essential scope or spirit of the invention, and accordingly it is intended to claim the same broadly as well as specifically as indicated by the appended claims.

We claim:

1. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a loope r, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination,

a. selectively actuatable thread puller means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread,

b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper,

c. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, and

d. thread clamping means effective to clamp the thread at a location between the needle and the thread tensioner after thread has been pulled from the thread supply and before severance of the thread.

2. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination,

a. selectively actuatable thread puller means comprising a piston and thread anti-deflection means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being efiective when actuated to pull a predetermined length of thread from thethread supply sufficient to prevent unthreading of the needle after severance of the thread, said piston being reciprocable between first and second positions and having at least one aperture therethrough through which freely passes the needle thread when said piston is in its said first position, and said thread anti-deflection means being operative to prevent more than a predetermined minimal lateral deflection of the main run of the thread when said piston is reciprocated from its said first position to its said second position to pull thread from the thread pp y b. thread clamp means partly carried by said reciprocable piston and partly carried in fixed position by the sewing machine effective to clamp the thread therebetween against longitudinal movement when said piston has moved to its second position,

c. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, and

d. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means.

3. Apparatus as defined in claim 2 wherein said thread puller and clamp means comprise, a reciprocable piston as aforesaid having secured to its free end the base wall of a U- shaped member with the arms of the U extending away from the piston and being transversely colinearly apertured to comprise the aforesaid at least one aperture, said anti-deflection means comprising a pair of pins disposed adjacent to and outwardly of the said arms of said U-shaped member and on the opposite side of the thread from the base wall of said U-shaped member, and said thread clamp means partly carried in fixed position by the sewing machine comprising a stop element disposed between the said arms of the said U-shaped member on the opposite side of said anti-deflection pins from the thread, while the thread clamp means partly carried by said piston comprises the said base wall of the U-shaped member.

4. Apparatus as defined in claim 3 wherein the said base wall of the said U-shaped member is faced with a thread engageable compressible pad.

5. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination,

a. selectively actuatable thread puller means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread,

b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper,

c. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to. then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, and

d. actuatable sewing machine bed dropping means operatively coupled to the sewing machine bed plate and to said control means, and actuatable by the latter when said control means is operated to drop the sewing machine bed plate after the thread has been severed by said thread severing means.

6. Apparatus as defined in claim 5 wherein said thread puller means and thread severing means and bed dropping means all comprise pneumatically actuated pistons to effect physical movement of the operative parts.

7. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination,

a. selectively actuatable thread puller means comprising a thread engageable movable element and a thread engageable anti-deflection means disposed respectively on opposite sides of the longitudinal run of the thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to-prevent unthreading of the needle after severance of the thread, said anti-deflection means being effective to prevent more than a predetermined minimal lateral deflection of the main run of the thread, said movable element when actuated by said control means as aforesaid being moved against the thread to thereby deflect a short thread interval laterally of the main run of the thread for a distance sufficient to pull from the thread supply the aforesaid predetermined length of thread,

b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper,

c. selectively operable control means operatively coupled to said thread puller means and thread severing means effec tive when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, and

d. thread clamping means effective to clamp the thread against longitudinal movement, said thread clamping means comprising a first part carried by said thread puller movable element and a second part carried in fixed position by the sewing machine, said first and second clamping means parts being so positioned relatively to one another that the thread is clamped therebetween when said thread puller movable element is actuated by said control means as aforesaid.

8. Apparatus as defined in claim 7 wherein said clamping means first part clamps the thread to said clamping means second part at the end of thread pulling movement of said thread puller movable element.

9. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination,

a. selectively actuatable thread puller means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when.

actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread,

b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, selectively operable control means operatively coupled to said thread puller means and thread severing means efiective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, said selectively operable control means comprising,

1. a needle positioner mechanism operatively coupled to the sewing machine needle and looper and effective to automatically move both the needle and looper into a particular position suitable for thread severing at the end of a stitching run if the needle and looper have not of themselves stopped at such particular position,

2. selectively operable first switch means effective when operated to actuate and thereafter deactuate both said thread puller means and said thread severing means, and

3. first inerlock means interconnecting said needle positioner mechanism and said first switch means effective to prevent operation of the latter if said needle positioner mechanism has not moved the needle and looper into the aforesaid particular position,

d. actuatable sewing machine bed dropping means operatively coupled to the sewing machine bed plate and to said control means first switch means and actuatable by the latter when said control means is operated to drop the sewing machine bed plate after the thread has been severed by said thread severing means.

10. Apparatus as defined in claim 9 further including second interlock means interconnecting said needle positioning mechanism and said first switch means effective to prevent actuation of said bed dropping means during operation of said needle positioning mechanism. 

1. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination, a. selectively actuatable thread puller means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread, b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, c. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, and d. thread clamping means effective to clamp the thread at a location between the needle and the thread tensioner after thread has been pulled from the thread supply and before severance of the thread.
 2. selectively operable first switch means effective when operated to actuate and thereafter deactuate both said thread puller means and said Thread severing means, and
 2. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination, a. selectively actuatable thread puller means comprising a piston and thread anti-deflection means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread, said piston being reciprocable between first and second positions and having at least one aperture therethrough through which freely passes the needle thread when said piston is in its said first position, and said thread anti-deflection means being operative to prevent more than a predetermined minimal lateral deflection of the main run of the thread when said piston is reciprocated from its said first position to its said second position to pull thread from the thread supply, b. thread clamp means partly carried by said reciprocable piston and partly carried in fixed position by the sewing machine effective to clamp the thread therebetween against longitudinal movement when said piston has moved to its second position, c. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, and d. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means.
 3. Apparatus as defined in claim 2 wherein said thread puller and clamp means comprise, a reciprocable piston as aforesaid having secured to its free end the base wall of a U-shaped member with the arms of the U extending away from the piston and being transversely colinearly apertured to comprise the aforesaid at least one aperture, said anti-deflection means comprising a pair of pins disposed adjacent to and outwardly of the said arms of said U-shaped member and on the opposite side of the thread from the base wall of said U-shaped member, and said thread clamp means partly carried in fixed position by the sewing machine comprising a stop element disposed between the said arms of the said U-shaped member on the opposite side of said anti-deflection pins from the thread, while the thread clamp means partly carried by said piston comprises the said base wall of the U-shaped member.
 3. first inerlock means interconnecting said needle positioner mechanism and said first switch means effective to prevent operation of the latter if said needle positioner mechanism has not moved the needle and looper into the aforesaid particular position, d. actuatable sewing machine bed dropping means operatively coupled to the sewing machine bed plate and to said control means first switch means and actuatable by the latter when said control means is operated to drop the sewing machine bed plate after the thread has been severed by said thread severing means.
 4. Apparatus as defined in claim 3 wherein the said base wall of the said U-shaped member is faced with a thread engageable compressible pad.
 5. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination, a. selectively actuatable thread puller means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread, b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, c. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, and d. actuatable sewing machine bed dropping means operatively coupled to the sewing machine bed plate and to said control means, and actuatable by the latter when said control means is operated to drop the sewing machine bed plate after the thread has been severed by said thread severing means.
 6. Apparatus as defined in claim 5 wherein said thread puller means and thread severing means and bed dropping means all comprise pneumatically actuated pistons to effect physical movement of the operative parts.
 7. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination, a. selectively actuatable thread puller means comprising a thread engageable movable element and a thread eNgageable anti-deflection means disposed respectively on opposite sides of the longitudinal run of the thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread, said anti-deflection means being effective to prevent more than a predetermined minimal lateral deflection of the main run of the thread, said movable element when actuated by said control means as aforesaid being moved against the thread to thereby deflect a short thread interval laterally of the main run of the thread for a distance sufficient to pull from the thread supply the aforesaid predetermined length of thread, b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, c. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, and d. thread clamping means effective to clamp the thread against longitudinal movement, said thread clamping means comprising a first part carried by said thread puller movable element and a second part carried in fixed position by the sewing machine, said first and second clamping means parts being so positioned relatively to one another that the thread is clamped therebetween when said thread puller movable element is actuated by said control means as aforesaid.
 8. Apparatus as defined in claim 7 wherein said clamping means first part clamps the thread to said clamping means second part at the end of thread pulling movement of said thread puller movable element.
 9. A thread severing apparatus for blind stitch sewing machines of the type having an oscillatable needle, a looper, a thread supply and thread tensioner, and a droppable work supporting bed plate, comprising in combination, a. selectively actuatable thread puller means operatively associated with the sewing machine needle thread at a location along the thread between the needle and the thread tensioner, said thread puller means being effective when actuated to pull a predetermined length of thread from the thread supply sufficient to prevent unthreading of the needle after severance of the thread, b. selectively actuatable thread severing means effective when actuated to sever the needle thread when the latter is held in a predetermined position by the sewing machine looper, c. selectively operable control means operatively coupled to said thread puller means and thread severing means effective when operated, and when the needle thread is held in a predetermined position by the sewing machine looper as aforesaid, to actuate said thread puller means and said thread severing means to first pull from the thread supply the aforesaid predetermined length of thread and to then sever the needle thread, and to thereafter deactuate said thread puller means and thread severing means, said selectively operable control means comprising,
 10. Apparatus as defined in claim 9 further including second interlock means interconnecting said needle positioning mechanism and said first switch means effective to prevent actuation of said bed dropping means during operation of said needle positioning mechanism. 